1) Field of the Invention
The present invention relates to an image forming apparatus, such as a copier, a printer, and a facsimile of electro photography-type or electrostatic-recording type, which can form images with two or more colors.
2) Description of the Related Art
In color image forming apparatuses, whether an image is to be formed in a monochrome mode or a color mode can be selected. Such an image forming apparatus includes an image formation unit corresponding to each color. Moreover, each image formation unit includes a photosensitive body.
When an image is to be formed in the color mode, for instance, the photosensitive body corresponding to black is not used. In a conventional image forming apparatus, when the image is to be formed in the color mode, for instance, the photosensitive body corresponding to black is physically separated from a transfer body to reduce friction between them and thus lengthen the life of the photosensitive body. However, there is a drawback in this technique, that the productivity lowers because there is a need to physically separate the photosensitive body from the transfer body.
Japanese Patent Application-Laid-Open No. 2000-293003 discloses an image forming apparatus that can surely, and at low power, perform switching between the color mode and the monochrome mode. Moreover, Japanese Patent Application-Laid-Open No. 2002-139887 discloses an image forming apparatus that decreases the running cost and the manufacturing cost by using a belt transfer device having a simpler structure.